in situ FTIR Spectroscopic Characterization of Absorbed Species on Carbon Electrode,Part II: TCNE Anion Radical from Acetonitrile Solution

The reduction of tetracyanoethylene (TCNE) to its anion radicals on glassy carbon has been studied using in situ FTIR spectroscopy. In contrast to its adsorption behavior on a platinum electrode, TCNE was found to adsorb on a carbon surface not only as the dianion but also as the tricyanovinyl alcoholate (TVA) ion. A mechanism for the formation of the TVA ion involving the presence of surface functional groups on the carbon electrode is proposed.     

Nanostructured copper particles-incorporated Nafion-modified electrode for oxygen reduction

The electrocatalytic activity of nanostructured copper particles (represented as Cu_nano) incorporated Nafion (Nf) film-coated glassy carbon (GC) electrode (GC/Nf/Cu_nano) towards oxygen reduction was investigated in oxygenated 0.1 M phosphate buffer (pH 7.2). The electrodeposited Cu_nano in Nf film was characterized by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The electrocatalytic activity of Cu_nano at the modified electrode towards oxygen reduction was studied using cyclic voltammetry technique. The molecular oxygen reduction at the GC/Nf/Cu_nano-modified electrode started at a more positive potential than at a bare GC electrode. A possible reaction mechanism was proposed in which oxygen reduction may proceed through two-step two-electron processes at the GC/Nf/Cu_nano electrode. The GC/Nf/Cunano electrode shows higher stability for oxygen reduction in neutral solution and the electrode may find applications in fuel cells.     

Glassy carbon layer formed in diamond-like carbon films with femtosecond laser pulses

We report the first observation, to our knowledge, of a glassy carbon (GC) layer modified from diamond-like carbon (DLC) films with femtosecond (fs) laser pulses. The GC layer, which is confirmed by Raman spectroscopy, is produced most efficiently at low laser fluence near the ablation threshold of the DLC films. This surface modification depends little on the laser polarization and wavelength used. The fs laser-induced GC layer should be a new thin-film material useful for a variety of engineering applications due to its characteristics similar to those of DLC and the additional properties inherent in GC. PACS 61.80.Ba; 79.20.Ds; 42.62.Cf     

A study on the reaction between chlorine trifluoride gas and glass-like carbon

The reaction between glass-like carbon (GC) and chlorine trifluoride (ClF₃) gas was investigated with weight measurements, surface analysis, and gas desorption measurements, where the ClF₃ gas is used for the in situ cleaning of tubes in silicon-related fabrication equipment. From Auger electron spectroscopy and X-ray photoelectron spectroscopy measurements, a carbon mono-fluoride, –(CF)_n–, film near the surface of GC is considered to be grown onto the GC surface above 400 °C by the chemical reaction with ClF₃, and this thickness of the fluoride film depends on the temperature. The grown fluoride film desorbs by annealing in a vacuum up to 600 °C. Although GC is apparently etched by ClF₃ over 600 °C, the etch rate of GC is much lower than that of SiC and quartz.     

Oxygen reduction activity of N-doped carbon-based films prepared by pulsed laser deposition

Carbon-based films with nitrogen species on their surface were prepared on a glassy carbon (GC) substrate for application as a non-platinum cathode catalyst for polymer electrolyte fuel cells. Cobalt and carbon were deposited in the presence of N₂ gas using a pulsed laser deposition method and then the metal Co was removed by HCl-washing treatment. Oxygen reduction reaction (ORR) activity was electrochemically determined using a rotating disk electrode system in which the film samples on the GC substrate were replaceable. The ORR activity increased with the temperature of the GC substrate during deposition. A carbon-based film prepared at 600 °C in the presence of N₂ at 66.7 Pa showed the highest ORR activity among the tested samples (0.66 V vs. NHE). This film was composed of amorphous carbons doped with pyridine type nitrogen atoms on its surface.     

Infrared reflection absorption study of carbon monoxide adsorption on Cu(1 0 0)-c(2 × 2)-Pd surfaces formed by palladium vacuum-depositions at various temperatures

Using infrared reflection absorption spectroscopy (IRRAS) and temperature programmed desorption (TPD), we investigated carbon monoxide (CO) adsorption and desorption behaviors on atomic checkerboard structures of Cu and Pd formed by Pd vacuum deposition at various temperatures of Cu(1 0 0). The 0.15-nm-thick Pd deposition onto a clean Cu(1 0 0) surface at room temperature (RT) showed a clear c(2 × 2) low-energy electron diffraction (LEED) pattern, i.e. Cu(1 0 0)-c(2 × 2)-Pd. The RT-CO exposure to the c(2 × 2) surfaces resulted in IRRAS absorption caused by CO adsorbed on the on-top sites of Pd. The LEED patterns of the Pd-deposited Cu(1 0 0) at higher substrate temperatures revealed less-contrasted c(2 × 2) patterns. The IRRAS intensities of the linearly bonded CO bands on 373-K-, 473-K-, and 673-K-deposited c(2 × 2) surfaces are, respectively, 25%, 22%, and 10% less intense than those on the RT-deposited surface, indicating that Pd coverages at the outermost c(2 × 2) surfaces decrease with increasing deposition temperature. In the initial stage of the 90-K-CO exposure to the RT surface, the band attributable to CO bonded to the Pd emerged at 2067 cm⁻¹ and shifted to higher frequencies with increasing CO exposure. At saturation coverage, the band was located at 2093 cm⁻¹. In contrast, two distinct bands around 2090 cm⁻¹ were apparent on the spectrum of the 473-K-deposited surface: the CO saturation spectrum was dominated by an apparent single absorption at 2090 cm⁻¹ for the 673-K-deposited surface. The TPD spectra of the surfaces showed peaks at around 200 and 300 K, which were ascribable respectively to Cu-CO and Pd-CO. Taking into account the TPD and IRRAS results, we discuss the adsorption-desorption behaviors of CO on the ordered checkerboard structures.     

ESR study of fullerene black

Fullerene black before and after annealing at 850°C has been studied by electron spin resonance (ESR). For initial fullerene black, the ESR line exhibits wide wings and its shape is caused by magnetic dipole-dipole interactions between radicals localized randomly on the carbon surface. Dioxygen decreases reversibly the amplitude of the ESR line without changes in its shape, width (0.19 mT) andg-factor (2.0022). This is explained by the assumption that dioxygen molecules adsorbed on the surface broaden strongly ESR lines only of neighboring radicals. For annealed fullerene black, the ESR line is Lorentzian, dioxygen reversibly broadens the line, and theg-factor decreases with the broadening of the line by dioxygen. This is explained by radical-radical and radical-dioxygen spin exchange interactions via conjugated bonds formed in the course of annealing. Flattening of curved carbon surfaces after annealing explains in a uniform way changes in parameters of ESR lines and in reactivity and catalytic activity of fullerene black.     

A voltammetric sensor based on GO–MWNTs hybrid nanomaterial-modified electrode for determination of carbendazim in soil and water samples

A voltammetric sensor for the determination of carbendazim was developed at a glassy carbon electrode modified with a hybrid nanomaterial (graphene oxide–multi-walled nanotubes/glassy carbon (GO–MWNTs/GC)). Its surface electrochemical property was studied with UV–Vis spectroscopy, TEM analysis, and electrochemical impedance spectroscopy. The electrochemical behavior of carbendazim was investigated on the modified electrode with cyclic voltammetry and differential pulse voltammetry. The influence of modifier dosage, buffer solution, pH, accumulation time, and scan rates on the determination was discussed. The results indicated that the reaction of carbendazim on the electrode was controlled by diffusion and was an irreversible process with two electrons. The effective area of GO–MWNTs/GC, anodic transfer coefficient, and apparent diffusion coefficient were calculated. The anodic peak current of carbendazim was linear with the concentration of carbendazim from 10 nM to 4 μM with a detection limit of 5 nM (S/N?=?3). The proposed sensor was successfully applied to the determination of carbendazim in soil and tap water.     

Electrochemistry of 4′-hydroxy and acetoxy flavones CV and NPP study

Electrochemical reduction behavior of 3-acetoxyflavone was compared with 3-hydroxyflavone on glassy carbon electrode with DMF and 60% DMF/Britton Robinson buffer at pH 3.8 & 10.1 using cyclic voltammetry (CV) and on dme using normal pulse polarography (NPP). Single irreversible reduction waves were observed due to the reduction of keto moiety. The effects of change in medium, pH and sweep rate were evaluated. The electrode process was found to be diffusion controlled and enhanced substituent effect was noticed due to extended conjugation. Kinetic parameters were calculated from CV & NPP measurements using R.S. Nicholson and I. Shain equation and Meites & Isreal equation, respectively. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Electron surface states in short-period superlattices: (GaAs)2/(AlAs)2(1 0 0)-c(4 × 4)

The electronic structure of (GaAs)₂/(AlAs)₂(1 0 0)-c(4 × 4) superlattice surfaces was studied by means of angular-resolved photoelectron spectroscopy (ARUPS) in the photon energy range 20-38 eV. Four samples with different surface termination layers were grown and As-capped by molecular beam epitaxy (MBE). ARUPS measurements were performed on decapped samples with perfect c(4 × 4) reconstructed surfaces. An intensive surface state was, for the first time, observed below the top of the valence band. This surface state was found to shift with superlattices’ different surface termination in agreement with theoretical predictions.     

超小金纳米团簇的电催化氧还原性质

Ultrasmall gold nanoclusters consisting of 2-4 Au atoms were synthesized and their performance in electrocatalytic oxygen reduction reactions (ORR) was examined. These clusters were synthesized by exposing AuPPh₃Cl to the aqueous ammonia medium for one week. Electrospray ionization mass spectrometry (ESI-MS), X-ray absorption fine structure (XAFS), and X-ray photoelectron spectroscopy (XPS) analyses indicate that the as-synthesized gold clusters (abbreviated as Au_x) consist of 2-4 Au atoms coordinated by the triphenylphosphine, hydroxyl, and adsorbed oxygen ligands. A glassy carbon disk electrode loaded with the Au_x clusters (Au_x/GC) was characterized by the cyclic and linear-sweep voltammetry for ORR. The cyclic voltammogram vs. RHE shows the onset potential of 0.87 V, and the kinetic parameters of J_K at 0.47 V and the electron-transfer number per oxygen molecule were calculated to be 14.28 mA/cm² and 3.96 via the Koutecky-Levich equations, respectively.     

Effect of carbon source on the carbothermal reduction for the fabrication of ZnO nanostructure

Surface area effect of carbon source on the carbothermal reduction for the fabrication of ZnO nanostructure was investigated. For a systematic comparison, graphite and three kinds of carbon black powder were used as source materials for the carbothermal reduction. Depending on the surface area, the carbothermal reduction at 800 °C for 30 min resulted in Zn-silicate island or ZnO nanorod at the same experimental condition. These structures were characterized with a scanning electron microscopy, a transmission electron microscopy, an energy dispersive spectroscopy and an X-ray photoelectron spectroscopy. The results show that the reducing power of ZnO_(s) source into Zn_(g) vapor is strongly dependent on the surface area of carbon source, and that the fabrication of ZnO nanostructure can be performed more efficiently by using carbon source with large surface area.     

光固定辣根过氧化酶修饰电极的直接电化学

用聚氨酯丙烯酸酯预聚体将辣根过氧化物酶用光固定法制备了辣根过氧化物酶修饰电极.采用循环伏安法研究了该电极在没有媒介体的条件下的电化学性质,并考察了其对H_2O_2的生物电催化活性.结果表明,该电极可以在没有媒介体存在的条件下进行直接而稳定的电子转移.扫描100圈后,扫描时的峰电流仍然几乎不变;在缓冲溶液中保存30天后,其伏安响应仍能保持保存前的约95%以上,且仍保持对H_2O_2电化学还原的生物电催化作用.这为酶电极的制备及酶的固定化提出了新方法.     

Effect of ferroelectric polarization on the adsorption and reaction of ethanol on BaTiO3

The effect of ferroelectric polarization on the adsorption and reaction of ethanol on BaTiO₃ was studied using temperature-programmed desorption (TPD). Consistent with previous studies for methanol, the reactive sticking coefficient for ethanol on the surfaces of the ferroelectric, tetragonal phase of BaTiO₃ was found to be dependent on the orientation of the ferroelectric domains with a higher sticking coefficient on the c⁺ surface relative to the c⁻ surface. TPD peak shapes and the relative product yields were also found to be polarization dependent suggesting that ferroelectric polarization may affect the intrinsic reactivity of the surface.     

Elemental composition of β-Sic(001) surface phases studied by medium energy ion scattering

β-SiC surfaces have been investigated in terms of surface composition and reconstruction by medium energy ion scattering (MEIS), Auger electron spectroscopy (AES), and low energy electron diffraction (LEED). A (3 × 2) phase is produced by evaporating Si on a β-SiC surface. Heat treatment at 1065°C causes consecutive transformation into (5 × 2), c(4 × 2), (2 × 1), (1 × 1) and c(2 × 2) phases. Quantitative analysis of MEIS spectra shows that the c(4 × 2) surface has a full silicon topmost layer, whereas the c(2 × 2) surface has a full carbon topmost layer. The (3 × 2) and (5 × 2) phases are believed to originate from additional Si dimer rows on top of a Si terminated crystal.     

Investigation on surface‐enhanced Raman scattering activity on an ex situ ORC roughened nickel electrode

Roughened nickel electrode surfaces have been demonstrated to exhibit a moderate enhanced Raman scattering effect with an enhancing factor of about 10⁴, which is not suitable in some cases for further inhibition adsorbates study. We reported here a new modified roughening procedure of nickel electrodes, by which a high S/N ratio surface‐enhanced Raman spectroscopy (SERS) of pyridine was obtained. At least two major advantages were found for the modified roughening methods: (1) enhancing factor was improved by a factor of about 10, (2) SERS‐active sites were distributed uniformly on the Ni surfaces. Potential‐dependent SERS spectra of a candidate inhibitor molecule benzotriazole (BTAH) adsorbed onto nickel electrodes were briefly presented for verifying the feasibility of the modified roughening method in this paper. Results showed that BTAH molecules were adsorbed on the nickel electrodes in neutral molecule form at more negative potentials and a polymer‐like film with the composition of [Ni_n(BTA)_p]_m formed on the nickel electrodes with the positive shift of potentials. Copyright © 2008 John Wiley & Sons, Ltd.     

Electrochemical properties of undoped CVD diamond films

The electrochemical properties of undoped diamond polycrystalline films grown on tungsten wire substrates using methanol as a precursor are described. The diamond film quality was changed by introducing sp²-bonded non-diamond carbon impurity through adjustment of the methanol-to-hydrogen (C/H) source gas ratio used for diamond growth.The electrodes were characterized by Raman spectroscopy, scanning electronic microscopy (SEM) and cyclic voltammetry (CV).Diamond coated tungsten wires were then used as a working electrode to ascertain their electrochemical behavior in electrolytic medium. Electrochemical windows of these films were found to be suitable in the potential range of [−2.5 V, +2.2 V] vs. Ag/AgCl in acid medium (0.1 M KCl).The electrochemical behavior was evaluated also using the Fe(CN)₆^3−/4−redox couple.The results demonstrate that the grain boundaries and sp²-hybridized carbon impurity can have a significant influence on electrochemical window of undoped diamond electrodes. It was observed that with increasing sp² carbon impurity concentration the electrochemical window decreases.     

Single-wall carbon nanotube chemical attachment at platinum electrodes

Self-assembled monolayer (SAM) techniques were used to adsorb 4-aminothiophenol (4-ATP) on platinum electrodes in order to obtain an amino-terminated SAM as the base for the chemical attachment of single-wall carbon nanotubes (SWCNTs). A physico-chemical, morphological and electrochemical characterizations of SWCNTs attached onto the modified Pt electrodes was done by using reflection-absorption infrared spectroscopy (RAIR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and cyclic voltammetry (CV) techniques. The SWNTs/4-ATP/Pt surface had regions of small, medium, and large thickness of carbon nanotubes with heights of 100-200 nm, 700 nm to 1.5 μm, and 1.0-3.0 μm, respectively. Cyclic voltammetries (CVs) in sulfuric acid demonstrated that attachment of SWNTs on 4-ATP/Pt is markedly stable, even after 30 potential cycles. CV in ruthenium hexamine was similar to bare Pt electrodes, suggesting that SWNTs assembly is similar to a closely packed microelectrode array.     

Optical anisotropy of GaNAs grown on GaAs(0 0 1) substrate

In this paper GaN_xAs_1−x surfaces during growth are observed using reflectance difference or reflectance anisotropy spectroscopy (RDS or RAS). The epi-layer was grown by solid-source molecular beam epitaxy (MBE) system with a RF nitrogen prasma source. RD spectra showed broader structure and reduced amplitude compared to those of GaAs surfaces; GaAs(2 × 4)-like features were still observed with weak and blue-shifted peaks. In the low growth temperature region, an extra structure was also observed around 3.02 eV. We proposed that GaN_xAs_1−x surface can be classified into three types of the surface.     

Thermal and photochemical reactivity of oxygen atoms on gold nanocluster surfaces

Reduction of oxidized gold nanoclusters by exposures to foreign gases and irradiation of UV photons has been investigated using X-ray photoelectron spectroscopy. Gold nanoclusters with narrow size distributions protected by alkanethiolate ligands were deposited on a TiO₂(1 1 0) surface with dip coating. Oxygen plasma etching was used for removal of alkanethiolate ligands and oxidization of gold clusters. The oxidized gold clusters were exposed to CO, C₂H₂, C₂H₄, H₂, and hydrogen atoms. Although, C₂H₄ and H₂ did not show any indications of reduction of oxidized gold clusters, CO, C₂H₂, and hydrogen atoms reduced the oxides on gold cluster surfaces. Among them, hydrogen atoms were most effective for reduction. Irradiation of UV photons around 400 nm could also reduce the oxidized gold clusters. The photochemical reduction mechanism was proposed as follows. The photo-reduction was initiated by electronic excitation of gold clusters and oxygen atoms activated reacted with carbon atoms at the surfaces of gold clusters. Carbon species were likely absorbed in gold clusters or remained at the boundaries between gold clusters when gold clusters agglomerated during oxygen plasma exposures. As the photochemical reduction progressed, carbon atoms segregated to the surfaces of gold clusters.